Liquid crystalline compounds and mixtures

ABSTRACT

Novel nematic liquid crystalline azo-compounds have been found, which are anisotropic over a wide temperature range which includes room temperature. 
     The compounds are temperature, light and moisture proof. They exhibit no dynamic scattering. The compounds may be employed in E.S.R. and N.M.R. spectroscopy, and, as the case may be mixed with other nematic liquid crystalline compounds, in displays.

This is a division of application Ser. No. 531,087, filed Dec. 9, 1974,now U.S. Pat. No. 3,984,392.

This invention relates to novel liquid crystalline compounds.

Many liquid crystalline compounds have too high a melting point or toosmall a liquid-crystalline temperature range for practical applications.

It is an object of the invention to provide nematic liquid crystallinecompounds, which are liquid crystalline over a wide temperature rangeand which melt below room temperature.

It has been found that compounds of the formula ##STR1## in which n hasthe value 6 or 7, and mixtures of said compounds are in conformity withthe object in view.

The compounds are temperature, light and hydrolysis proof. They exhibitno dynamic scattering. The compounds can be applied as solvents inE.S.R. and N.M.R.-spectrocopy. Furthermore, they may be employed indisplays, as the case may be mixed with other liquid crystallinecompounds, for example nematic liquid crystalline compounds whichexhibit dynamic scattering. Examples of nematic liquid crystallinecompounds which may be mixed with the compounds according to theinvention are the compounds described in French Patent Specification1,537,000, the published Netherlands Patent Application 7,007,912, andthe published German Patent Applications 1,928,242; 2,017,727 and2,038,780.

The invention relates to novel compounds of the formula ##STR2## where n= 6 or 7 and to mixtures which contain at least one of said compounds.

It is to be noted that in Molecular Crystals and Liquid Crystals 11187-189 (1970) o-hydroxy-p-methoxybenzyl-p-n.butylanilide is describedas a nematic liquid crystalline compound. Said compound however, has amelting point of 44° C. It is true that the substance is liquidcrystalline up to 64.5° C and below the melting point to 8° C, but thesubstance already crystalline in a thin layer at 26° C.

The azo-compound which corresponds to said compound,p-n.butyl-o'-hydroxy-p'-methoxyazobenzene even appears to melt at astill higher temperature, 68° C, and to be liquid crystalline inundercooled condition only, to 60° C.

Hence it is the more surprising that the compounds of the formula 1 andmixtures formed therewith are liquid crystalline at room temperature andare liquid crystalline over a very wide range.

The surprising properties of the compounds found are illustrated by thetable below

    ______________________________________                                         ##STR3##                                                                                             melting                                               R         C.sub.m H.sub.2m+1                                                                          point ° C                                                                       T.sub.c ° C                           ______________________________________                                        N = C     CH.sub.3      44       64.5                                         N = N     CH.sub.3      68       60                                           N = N     n . C.sub.6 H.sub.13                                                                        8*       82     I                                     N = N     n . C.sub.7 H.sub.15                                                                        22-23    79     II                                    35.05 mol % I + 64.95 mol % II                                                                     9-15    75                                               49.64 mol % I + 50.034 mol % II                                                                   8.5-13   75                                               70.15 mol % I + 29.85 mol % II                                                                    0-2      75                                               ______________________________________                                         *A second crystal modification melts at 17° C.                    

The compounds of the formula 1 can be obtained in accordance withmethods known per se.

For example the compounds may be prepared by reacting o,p-dihydroxy-p'-butylazobenzene or an alkalimetal salt thereof with analkylhalogenide of the formula 2

    C.sub.n H.sub.2n+1 X                                       (2)

where n is 6 or 7 and X represents an iodine or bromine atom. Thereaction is preferably performed in a highly polar aprotic solvent, suchas for example dimethylformamide, at temperatures between roomtemperature and the boiling point of the mixture.

The azobenzene compound which is the starting point of said reaction isobtained by reacting p-butylphenyl-diazoniumtetra-fluoroborate withresorcinol in acetone/water between 0° and 5° C.

The compounds according to the invention and mixtures of nematicliquid-crystalline compounds with at least one of the compoundsaccording to the invention may be successfully employed in displaycells. Hence, the invention also relates to a display cell provided withat least two electrodes and a nematic liquid crystalline materialdisposed therebetween, characterized in that the liquid crystallinematerial contains at least one or more of the compounds of the formula1.

The invention is explained in more detail with reference to thefollowing examples.

1a)

To 0.1 mol of p-n.butylaniline in 40 ml of water 30 ml of concentratedHCl were added whilst stirring. Subsequently the reaction mixture wascooled at 0° C. To said mixture 0.1 mol of sodium nitrite, dissolved inwater were added whilst stirring, so that the temperature of thereaction mixture remained between 0° C and 5° C. After adding the sodiumnitrite solution stirring was continued for 15 minutes. Subsequently,0.15 mol of ammoniumborofluoride dissolved in water, were added to saidreaction mixture. The precipitated diazoniumborofluoride was filteredoff and washed with cold water after being kept in the refrigerator forone hour. The diazoniumborofluoride was dissolved in a mixture of 100 mlof water and acetone (1 : 1). Subsequently 0.15 mol of resorcinol,solved in 120 ml of water, were added. Said solution was kept in therefrigerator for 16 hours and subsequently poured into 500 ml of water.The resultant precipitate of 4-n-butyl-2', 4'-dihydroxyazobenzene wasfiltered off.

b)

0.10 mol of 4-n.butyl-2',4'-dihydroxyazobenzene were dissolved in 200 mlof methanol and 0.1 mol of potassium hydroxide were added. The mixturewas heated until the potassium hydroxide had fully dissolved.Subsequently, the methanol was removed in vacuum. To the residue of 50ml of abs.ethanol and 50 ml of benzene were added. The solvents wereextracted in vacuum. Said procedure was repeated twice. Finally, theresidue was taken up in petr.ether and the precipitate was filtered off.

c)

0.05 mol of the potassium salt of 4-n.butyl-2',4'-dihydroxyazobenzenewere dissolved in 300 ml of dimethylformamide. To this 0.05 mol ofn.hexyliodide were added whilst stirring and subsequently heated to 110°C. After the mixture had been kept at this temperature for 30 minutes,0.025 mol of n.hexyliodide were added and the mixture was stored foranother 45 minutes at 110° C. Finally, the reaction mixture was pouredout in water and shaked with petroleum ether. The petroleum etherextract was dried on a molecular sieve with a pore size of 4 A. Thepetroleum ether was removed in vacuo. The oily residue wasre-crystallized twice from abs. ethanol. Melting point 8° C.

2) In a similar way as in example 1c4-n.butyl-2'-hydroxy-4'-n.heptyloxyazobenzene was obtained starting fromthe potassium salt of 4-n.butyl-2',4'-dihydroxyazobenzene andn.heptyliodide. Melting point 22°-23° C.

3)

A glass plate measuring 60 × 65 × 2 mm (1 in FIGS. 1 and 2) which wasprovided with an 8-shaped pattern of indium oxide (thickness of layer0.1 nm) consisting of 7 segments 2, and a second glass plate 3 measuring50×60×1 mm which was covered with a tin oxide layer 4 having a thicknessof 0.1 nm, were rubbed in one direction, with a piece of lens paper atthe oxide-coated side, namely glass plate 1 in the longitudinaldirection and the glass plate 3 in the transverse direction.

On glass plate 1 two polythene strips were placed of a thickness of 20nm, onto which glass plate 3 was placed. The glass plates were connectedwith an epoxy glue, filling openings 7 being left. The space between theglass plates was subsequently filled withp-n.butyl-o'-hydroxy-p'-n.hexyloxyazobenzene. The openings 7 were closedwith epoxy glue.

To the connection points 8 which consisted of indium oxide, as well ason the part of glass plate 3 which extended beyond the glass plate 1,current supply leads were fitted. The underside of glass plate 1 and theupper side of glass plate 3 were provided with a polarising filter. Thedirection of polarisation of the two filters was parallel to thedirection in which plate 1 had been rubbed with lens paper. The displaycell thus obtained when viewed through showed a dark image field.

At the oxide-coated surface of the glass plates, the molecules of thenematic liquid crystalline substance are disposed parallel to thesurface and in the direction of rubbing. Since said directions areperpendicular to each other, the liquid crystalline layer has a twistedstructure.

Across the glass plate 3 and the segments on plate 1 an alternatingvoltage of 6 V, 50 Hz was applied. This yielded a bright 8-shaped image.At the location of the segments 2 the molecules are orientedperpendicular to the surface of the glass plates, so that the cellbecomes locally transparent.

FIG. 1 shows a plane view of the display cell before the polarisationfilters were mounted, while FIG. 2 is a cross-section taken at the lineA-B after the filters were mounted.

What is claimed is:
 1. An orientation-type liquid crystal display cellhaving a layer of a liquid crystal material disposed between a pair ofelectrodes, at least one of which is transparent, wherein said liquidcrystal material consists essentially of at least one compound of theformula ##STR4## wherein n is 6 or 7.